1. Field of the Invention
The invention concerns a bicycle rear suspension intended, notably for off-road operation.
2. Discussion of the Background
The rear wheels of this type of bicycle are generally connected to the bicycle frame by shock absorption means in both rear and front, in order to reduce the intensity of the forces and vibrations transmitted to the cyclist, which ensures improved comfort as well as better control of the bicycle.
U.S. Pat. No. 3,931,990 describes a bicycle with oscillating suspension of the rear wheel, connected to a spring and to a shock absorber. With such a suspension, only a fraction of the power delivered by the cyclist on each pedal stroke is used for forward movement of the bicycle, the complementary fraction being lost on compression of the rear suspension resulting from the transfer of weight.
The invention concerns, more particularly, a bicycle rear suspension, of the type comprising a lower fork pivotally mounted in the crank gear case of a bicycle frame, and at its other end an upper fork, which bears a wheel driven in rotation by a chain, and the upper end of which is pivotally mounted on the end of an arm whose other end is pivotally mounted on the frame.
Thus, by positioning the pivoting points of the lower and upper forks in the manner described, the compression of the suspension resulting from the transfer of weight on pedaling is not only neutralized, but even overcompensated, which secures, among other advantages, preservation of all of the shock absorption potential of the suspension.
For that purpose, the suspension according to the invention is characterized in that the vertices of the articulated quadrilateral delimited by the lower and upper forks, the arm and the frame are so arranged that the straight line passing through the axis of rotation of the hub of the rear wheel, on the one hand, and the center of curvature of the path of said hub on clearance of the suspension, on the other, forms with a horizontal line extending parallel to the median longitudinal plane of the bicycle an angle ranging between 10xc2x0 and 20xc2x0.
According to another characteristic of this invention, the straight line passing through the axis of rotation of the hub of the rear wheel, on the one hand, and the center of curvature of the path of said hub on clearance of the suspension, on the other, forms with a horizontal line extending parallel to the median longitudinal plane of the bicycle an angle roughly equal to 14xc2x0.
According to another characteristic of this invention, the center of curvature of the path of the hub of the rear wheel is situated in proximity to the horizontal plane containing the upper part of the drive chain of the wheel.
According to another characteristic of this invention, the arm is all in one piece with a control lever of a shock absorption assembly.
According to another characteristic of this invention, the arm and the lever extend in directions forming an obtuse angle between them.
According to another characteristic of this invention, a shock absorption assembly is inserted between the saddle tube and the end of the lever opposite the pivoting point.
According to another characteristic of this invention, the pivoting point of the lower fork on the frame is situated above the axis of the crank gear case.
According to another characteristic of this invention, the pivoting point of the lower fork on the frame is situated in front of the axis of the crank gear case.
According to another characteristic of this invention, the pivoting point of the lower fork on the frame is placed above a horizontal line passing through the axes of rotation of the front and rear wheels.
According to another characteristic of this invention, the connecting point of the lower fork and upper fork is situated above a horizontal line passing through the axis of the crank gear case.
According to another characteristic of this invention, the connecting point of the upper fork and arm is placed in front of the point and above the latter.
According to another characteristic of this invention, the pivoting point, common to the lever and arm on the frame, is situated behind the point.